This summer's recommendations by the billionaire founder and philanthropist tackle some big questions.

Bill Gates is a voracious reader of massive proportions. According to an interview he had with the New York Times, he devours about 50 books per year.

Unlike the one or two books I pack when traveling, Gates takes a big canvas tote-bag of books with him whenever he goes on vacation. When asked by Time magazine whether reading is what has led to his success, Gates replied, "Absolutely. You don't really start getting old until you stop learning. Every book teaches me something new or helps me see things differently. Reading fuels a sense of curiosity about the world, which I think helped drive me forward in my career and in the work that I do now with my foundation."

As is customary every year, Gates recently published his list of summer book recommendations. He acknowledges that the selected choices are not light-reading -- these books wrestle with some big questions.

Gates says that if you liked Isaacson's other major biographies of Steve Jobs and Albert Einstein, you'll probably appreciate this one. "Isaacson does the best job I've seen of pulling together the different strands of Leonardo's life and explaining what made him so exceptional," writes Gates.

Bowler, a professor at Duke Divinity School, rejects the idea that we need a reason for everything that happens. But she also rejects the nihilist alternative. Gates writes, "When Bowler is diagnosed with stage IV colon cancer, she sets out to understand why it happened. Is it a test of her character? The result is a heartbreaking, surprisingly funny memoir about faith and coming to grips with your own mortality."

This is not an easy novel to read, but clues us in to Gates' eclectic (and even, dark) taste for books. Lincoln in the Bardo follows Abraham Lincoln's beloved eleven-year-old son, Willie Lincoln, and his acceptance of the afterlife--the Bardo--after he falls ill and dies. Gates writes. "It blends historical facts from the Civil War with fantastical elements--it's basically a long conversation among 166 ghosts, including Lincoln's deceased son. I got new insight into the way Lincoln must have been crushed by the weight of both grief and responsibility. This is one of those fascinating, ambiguous books you'll want to discuss with a friend when you're done."

This book gives the reader an overall view of the origin of humanity by synthesizing science and history in a quick easy read. Gates writes, "David created my favorite course of all time, Big History. It tells the story of the universe from the big bang to today's complex societies, weaving together insights and evidence from various disciplines into a single narrative."

In Factfulness, the late global TED phenomenon, Hans Rosling, reveals the ten instincts that distort our perspective -- from our tendency to divide the world into two camps (usually some version of us and them) to the way we consume media (where fear rules). In his book review, Gates called it "one of the best books I've ever read." He writes: "Hans gives you a breakthrough way of understanding basic truths about the world--how life is getting better, and where the world still needs to improve."